So someone made a post on FEH about the Sage/D-free situation, and the post clearly shows that another Dokkan youtuber, DG Gamer is involved, and the operation is conducted primarily on a discord formerly called "DG free", which is created by D-free and DG Gamer.

Interestingly enough, if you look look at Sagemaster's comment, he says it's DGFree who contacted him. This could be a mistake, and FEH post above shows a discord chat where DG Gamers says it was him who approached Sage.

I looked for "DGfree" on youtube and found several videos. I found one in Russian and Arabic language, and they all look like vendors for various IGCs and bitcoins. They both have link for DGfree's RU site, which is no longer working. If this is all connected to DG Free from the discord, then he probably has a pretty big operation covering wide range of IGC and virtual currencies, and he is not just a Gacha game IGC vendor.

Also if you look at the discord chat linked in the post above, you'll find that DG Gamer is giving instruction to D-free on how to handle the situation and they were still in contact with each other after Sagemaster issued his YT apology.

d-free took dow feh so reddit wouldnt attack our discord

just txted him

yea i told him to spent out for a week or so

since he will be getting alot of trolls since sage threw them his way lol

d-free will be back just stepped out for a min to avoid sage trolls

he doesnt want our discord getting flamed lol

So to sum it up, there is a vendor (possibly from Russian origin who goes by the name DGfree), and DG Gamer is promoting this vendor through discord created by D-free/DG Gamer and on his youtube Channel. D-free has also used DGfree's services, and he also talks about the vendor in his FEH video(which he took down right after Sagemaster went public with his apology). Sagemaster15 was approached by DGfree to be a sponsor, and D-free has vouched for the vendor when asked by Sagemaster. At this point, it looks like D-free is taking orders/collaborating with DG Gamers about how he is going to do damage control, and has not made public announcement in his YT/Twitter so far.

TL;DR If you check out D-free and DG Gamer's Dokkan content, and have heard about third party vendor and/or heard about DGfree, be warned.